Not sure if that was a 22 or 25, but it looks to shoot 3 mags on a fill (18 shots). It also seems like the first 6 or 8 had the most kick to them, with a gradual drop off.
Is that a hammer spring adjustment behind the receiver? Looks like a flathead screwdriver adjustable bit.
Going to be a tough choice between 22 and 25. You're going to want penetration with some H&N Hornets or similar type of ammo. It was certainly blasting chunks out of those wood pallets.
Now lets take a look at the Evanix ARP-6 revolver. Only available in 22, so you would assume the Viper with the 25 option is more powerful. The 22 ARP-6 is also a 200 bar gun versus 250 bar on the Viper. ARP-6 is good for 22.1 FPE according to Evanix.
This is making me think the Viper 22 should be easily mid to high 20's and the 25 should easily do 30 fpe. If that's the case, take my money.